(1) Field of the Invention
This invention relates to an apparatus and a method for inspecting masks which comprise transparent phase shifting mask elements using die-to-database inspection and a single image detector.
(2) Description of the Related Art
Inspection of phase shifting mask elements is a problem because defects are not readily apparent in the transparent phase shifting material. Masks can be inspected in a die-to-die mode, where comparisons between two identical die patterns are made, and in a die-to-database mode where comparisons are made between the die pattern and the image database. A method and apparatus which can perform this inspection using die-to-database methods has the advantage of a comparison directly to the design data.
A Patent Application TSMC-97-013; Ser. No. 09/177,340; Filed Oct. 13, 1998; entitled "A NEW APPARATUS AND METHOD FOR INSPECTING PHASE SHIFTING MASKS"; and assigned to the same Assignee describes an apparatus and method for die-to-die inspection of masks having phase shifting elements.
U.S. Pat. No. 5,737,072 to Emery et al. describes a method and apparatus for inspecting masks having phase shifting elements using transmitted and reflected light signals and signals derived from them.
U.S. Pat. No. 5,572,598 to Wihl et al. describes an inspection apparatus for inspecting masks having phase shifting elements which comprises a transmission light detector and a reflected light detector. The apparatus can be used for die-to-die comparison as well as die-to-database comparison.
U.S. Pat. No. 5,717,204 to Meisburger et al. describes an inspection system for masks having phase shifting elements using electron beam microscopy. An electron beam is scanned across the mask and detectors are used to measure the secondary and backscattered charged particles from the surface of the mask.
U.S. Pat. No. 4,926,489 Danielson et al. describes an automatic injection system for inspecting a reticle or photomask.
U.S. Pat. No. 4,805,123 to Specht et al. describes an inspection system for die-to-die system for inspecting a photomask or reticle.
U.S. Pat. No. 4,579,455 to Levy et al. describes an inspection apparatus and method for inspecting photomasks by comparison of duplicate die patterns.
U.S. Pat. No. 5,515,189 to Kuratomi et al. describes an image recognition system for optical masks.